Various surgical procedures require suturing or joining of adjacent portions of a patient's tissues. In a gastrointestinal anastomosis, for example, two portions of tubular intestine are joined to form a single tubular body by disposing the two portions in parallel relationship, making a longitudinal cut through contacting walls of the two portions and suturing the edges of the two portions together along each side of the cut. Suturing of tissue along a linear zone is also performed on a number of other body organs in other surgical procedures.
Such medical procedures have been greatly facilitated by the use of stapling instruments to perform the suturing operation. Staplers of this kind have a pair of jaw or beam members with forward regions that define a thin gap in which the tissue is received and clamped. One of more rows of staples are contained within one of the beam members and an actuator is manually traveled along the instrument to sequentially force the staples out of the beam member and into the adjacent tissue. The other beam member has indentations shaped to bend and close the staples as they penetrate through the tissue. In some instruments of this type, parallel rows of staples are implanted simultaneously and the same movement of the actuator travels a knife edge along the tissue between the rows of staples to perform a tissue cutting operation concurrently with the implanting of staples.
The two beam members are usually separable to facilitate emplacement of the instrument. A lower beam member is placed under the tissue that is to be sutured and then the upper member is placed over the the tissue and coupled to the lower member by latching means located at an intermediate region along the the members. The latching means in conjunction with a small spacer projection located near the tip of one of the beam members spaces the forward portions of the beam members apart a small distance to establish a tissue receiving gap between the members.
The tissue receiving gap should be of a predetermined uniform size along the length of the gap during the stapling operation to assure that all staples are uniformly deformed into the optimum closed configuration. If the beam members in the region of the gap are not parallel at that time, compression of the successive staples is not uniform. Crunched staples and/or inadequately closed staples may be formed at different regions along the gap.
Maintaining a uniform tissue gap has been found to be difficult as there is a tendency for the tips of the beam members to be spread apart by forces which arise during the clamping of tissue and as a result of the forcing of staples through the tissue. The tissue thickness may vary from patient to patient and at different areas of a particular patients anatomy. The clamped tissue exerts a load force on the beam members that tends to deflect the members away from each other and this force becomes greater when the tissue is thicker than the instrument was designed for. Closing of the staples also tends to spread the beam members as significant force must be exerted in order to deform the staples into the closed configuration.
As the forward portions of the beam members are in an essentially cantilevered relationship, undesirable spreading of the tips becomes particularly pronounced if the length of the beam members and the tissue gap is increased as would be desirable for some surgical procedures.
Mechanisms have heretofore been devised for the purpose of assuring that the staples are uniformly formed into the optimum closed configuration along the length of the tissue receiving gap. Some prior surgical staplers with such mechanisms are effective for this purpose only if the clamped tissue has a thickness closely conforming to the thickness for which the instrument was designed. Other prior instruments of this type are more tolerant of variations of tissue thickness but have mechanism for resisting beam spreading that operates through the actuator which the surgeon travels along the instrument to sequentially implant the staples. This undesirably adds to the force which the surgeon must exert and may, under extreme loading conditions, create uncertain or misleading tactile feedback to the surgeon. Under those conditions, such mechanisms may create sudden and unanticipated increases in resistance to actuator travel. Among other effects, this can create the impression that stapling has been completed when that is not in fact the case.
The present invention is directed to overcoming one or more of the problems discussed above.